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A novel dual-layer grating coupler was designed for efficient vertical coupling between a single-mode fiber and silicon nanowires, with characteristics of polarization diversity and both wavelength bands of 1.3 and 1.55 μm. Theoretical analysis and two-dimensional finite-difference time-domain simulations were applied to verify the performance of the design. Optimized results show that the coupling efficiencies of a dual-port output of 41% (−3.87 dB) for transverse-electric polarization at 1.56 μm, 32.88% (−4.83 dB) for transverse-magnetic (TM) polarization at 1.58 μm, and 27.06% (−5.68 dB) for TM polarization at 1.32 μm can be achieved. Dual-layer Fabry–Perot resonance was also investigated for high coupling efficiency.

A compact, highly efficient optical coupler for dielectric slot waveguides and hybrid plasmonic waveguides based on transition layers (air slot grooves) was investigated. The power-coupling efficiency of 75% for the direct coupling case increased to 90% following the insertion of an intermediate section. By performing time-averaged Poynting vector analysis, we successfully separated the factors of transmission, reflection, and radiation at the coupler interface. We found that the insertion of optimal air grooves into the coupler structure contributed to the improvement of coupling performance. The proposed compact structure is characterized by a high transmission efficiency, low reflection, small length, and broad-band spectrum response.

We investigated the potential application of planar chiral metamaterials (PCMs) to near infrared wavelength filters for multispectral measurement through electromagnetic simulation. PCM assumed here was a two-dimensional sub-wavelength surface grating on a high index film with chiral unit cells. The PCM exhibits optical activity (OA) for normally incident light at a finite wavelength range. Thus, by sandwiching the PCM with a pair of linear polarizers, a polarization interference-type BPF can be constructed. We focused on an all-dielectric PCM consisting of a silicon chiral layer and a dielectric underclad layer on a silica substrate. Wavelength filtering characteristics with different bandwidths have been verified for several underclad materials such as Si 3 N 4 , Al 2 O 3 , and Si.

We propose and numerically analyze a unique optical waveguide crossing based on a silicon-on-insulator (SOI) slab waveguide structure. The optical waveguide crossing consisting of four curved mirrors made of silica walls and beam spot-size converters formed in a silicon core layer of the SOI slab waveguide. Based on our design with a device footprint of 15 × 15 μm2, we obtained excellent device performances such as insertion loss of −0.3 dB, crosstalk of less than −35 dB in the wavelength range from 1.25 μm to 1.6 μm with the 3D-FDTD simulation.